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a8fabb3852
In case a user process using xenbus has open transactions and is killed
e.g. via ctrl-C the following cleanup of the allocated resources might
result in a deadlock due to trying to end a transaction in the xenbus
worker thread:
[ 2551.474706] INFO: task xenbus:37 blocked for more than 120 seconds.
[ 2551.492215] Tainted: P OE 5.0.0-29-generic #5
[ 2551.510263] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 2551.528585] xenbus D 0 37 2 0x80000080
[ 2551.528590] Call Trace:
[ 2551.528603] __schedule+0x2c0/0x870
[ 2551.528606] ? _cond_resched+0x19/0x40
[ 2551.528632] schedule+0x2c/0x70
[ 2551.528637] xs_talkv+0x1ec/0x2b0
[ 2551.528642] ? wait_woken+0x80/0x80
[ 2551.528645] xs_single+0x53/0x80
[ 2551.528648] xenbus_transaction_end+0x3b/0x70
[ 2551.528651] xenbus_file_free+0x5a/0x160
[ 2551.528654] xenbus_dev_queue_reply+0xc4/0x220
[ 2551.528657] xenbus_thread+0x7de/0x880
[ 2551.528660] ? wait_woken+0x80/0x80
[ 2551.528665] kthread+0x121/0x140
[ 2551.528667] ? xb_read+0x1d0/0x1d0
[ 2551.528670] ? kthread_park+0x90/0x90
[ 2551.528673] ret_from_fork+0x35/0x40
Fix this by doing the cleanup via a workqueue instead.
Reported-by: James Dingwall <james@dingwall.me.uk>
Fixes: fd8aa9095a
("xen: optimize xenbus driver for multiple concurrent xenstore accesses")
Cc: <stable@vger.kernel.org> # 4.11
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
726 lines
17 KiB
C
726 lines
17 KiB
C
/*
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* Driver giving user-space access to the kernel's xenbus connection
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* to xenstore.
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*
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* Copyright (c) 2005, Christian Limpach
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* Copyright (c) 2005, Rusty Russell, IBM Corporation
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License version 2
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* as published by the Free Software Foundation; or, when distributed
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* separately from the Linux kernel or incorporated into other
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* software packages, subject to the following license:
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this source file (the "Software"), to deal in the Software without
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* restriction, including without limitation the rights to use, copy, modify,
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* merge, publish, distribute, sublicense, and/or sell copies of the Software,
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* and to permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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* IN THE SOFTWARE.
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*
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* Changes:
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* 2008-10-07 Alex Zeffertt Replaced /proc/xen/xenbus with xenfs filesystem
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* and /proc/xen compatibility mount point.
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* Turned xenfs into a loadable module.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/kernel.h>
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#include <linux/errno.h>
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#include <linux/uio.h>
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#include <linux/notifier.h>
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#include <linux/wait.h>
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#include <linux/fs.h>
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#include <linux/poll.h>
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#include <linux/mutex.h>
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#include <linux/sched.h>
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#include <linux/spinlock.h>
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#include <linux/mount.h>
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#include <linux/pagemap.h>
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#include <linux/uaccess.h>
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#include <linux/init.h>
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#include <linux/namei.h>
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#include <linux/string.h>
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#include <linux/slab.h>
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#include <linux/miscdevice.h>
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#include <linux/workqueue.h>
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#include <xen/xenbus.h>
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#include <xen/xen.h>
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#include <asm/xen/hypervisor.h>
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#include "xenbus.h"
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unsigned int xb_dev_generation_id;
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/*
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* An element of a list of outstanding transactions, for which we're
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* still waiting a reply.
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*/
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struct xenbus_transaction_holder {
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struct list_head list;
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struct xenbus_transaction handle;
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unsigned int generation_id;
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};
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/*
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* A buffer of data on the queue.
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*/
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struct read_buffer {
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struct list_head list;
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unsigned int cons;
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unsigned int len;
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char msg[];
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};
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struct xenbus_file_priv {
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/*
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* msgbuffer_mutex is held while partial requests are built up
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* and complete requests are acted on. It therefore protects
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* the "transactions" and "watches" lists, and the partial
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* request length and buffer.
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*
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* reply_mutex protects the reply being built up to return to
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* usermode. It nests inside msgbuffer_mutex but may be held
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* alone during a watch callback.
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*/
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struct mutex msgbuffer_mutex;
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/* In-progress transactions */
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struct list_head transactions;
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/* Active watches. */
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struct list_head watches;
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/* Partial request. */
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unsigned int len;
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union {
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struct xsd_sockmsg msg;
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char buffer[XENSTORE_PAYLOAD_MAX];
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} u;
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/* Response queue. */
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struct mutex reply_mutex;
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struct list_head read_buffers;
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wait_queue_head_t read_waitq;
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struct kref kref;
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struct work_struct wq;
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};
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/* Read out any raw xenbus messages queued up. */
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static ssize_t xenbus_file_read(struct file *filp,
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char __user *ubuf,
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size_t len, loff_t *ppos)
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{
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struct xenbus_file_priv *u = filp->private_data;
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struct read_buffer *rb;
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unsigned i;
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int ret;
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mutex_lock(&u->reply_mutex);
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again:
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while (list_empty(&u->read_buffers)) {
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mutex_unlock(&u->reply_mutex);
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if (filp->f_flags & O_NONBLOCK)
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return -EAGAIN;
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ret = wait_event_interruptible(u->read_waitq,
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!list_empty(&u->read_buffers));
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if (ret)
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return ret;
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mutex_lock(&u->reply_mutex);
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}
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rb = list_entry(u->read_buffers.next, struct read_buffer, list);
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i = 0;
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while (i < len) {
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unsigned sz = min((unsigned)len - i, rb->len - rb->cons);
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ret = copy_to_user(ubuf + i, &rb->msg[rb->cons], sz);
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i += sz - ret;
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rb->cons += sz - ret;
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if (ret != 0) {
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if (i == 0)
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i = -EFAULT;
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goto out;
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}
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/* Clear out buffer if it has been consumed */
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if (rb->cons == rb->len) {
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list_del(&rb->list);
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kfree(rb);
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if (list_empty(&u->read_buffers))
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break;
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rb = list_entry(u->read_buffers.next,
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struct read_buffer, list);
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}
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}
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if (i == 0)
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goto again;
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out:
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mutex_unlock(&u->reply_mutex);
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return i;
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}
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/*
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* Add a buffer to the queue. Caller must hold the appropriate lock
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* if the queue is not local. (Commonly the caller will build up
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* multiple queued buffers on a temporary local list, and then add it
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* to the appropriate list under lock once all the buffers have een
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* successfully allocated.)
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*/
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static int queue_reply(struct list_head *queue, const void *data, size_t len)
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{
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struct read_buffer *rb;
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if (len == 0)
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return 0;
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if (len > XENSTORE_PAYLOAD_MAX)
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return -EINVAL;
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rb = kmalloc(sizeof(*rb) + len, GFP_KERNEL);
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if (rb == NULL)
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return -ENOMEM;
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rb->cons = 0;
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rb->len = len;
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memcpy(rb->msg, data, len);
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list_add_tail(&rb->list, queue);
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return 0;
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}
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/*
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* Free all the read_buffer s on a list.
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* Caller must have sole reference to list.
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*/
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static void queue_cleanup(struct list_head *list)
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{
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struct read_buffer *rb;
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while (!list_empty(list)) {
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rb = list_entry(list->next, struct read_buffer, list);
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list_del(list->next);
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kfree(rb);
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}
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}
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struct watch_adapter {
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struct list_head list;
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struct xenbus_watch watch;
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struct xenbus_file_priv *dev_data;
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char *token;
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};
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static void free_watch_adapter(struct watch_adapter *watch)
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{
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kfree(watch->watch.node);
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kfree(watch->token);
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kfree(watch);
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}
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static struct watch_adapter *alloc_watch_adapter(const char *path,
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const char *token)
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{
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struct watch_adapter *watch;
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watch = kzalloc(sizeof(*watch), GFP_KERNEL);
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if (watch == NULL)
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goto out_fail;
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watch->watch.node = kstrdup(path, GFP_KERNEL);
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if (watch->watch.node == NULL)
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goto out_free;
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watch->token = kstrdup(token, GFP_KERNEL);
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if (watch->token == NULL)
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goto out_free;
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return watch;
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out_free:
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free_watch_adapter(watch);
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out_fail:
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return NULL;
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}
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static void watch_fired(struct xenbus_watch *watch,
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const char *path,
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const char *token)
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{
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struct watch_adapter *adap;
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struct xsd_sockmsg hdr;
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const char *token_caller;
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int path_len, tok_len, body_len;
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int ret;
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LIST_HEAD(staging_q);
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adap = container_of(watch, struct watch_adapter, watch);
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token_caller = adap->token;
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path_len = strlen(path) + 1;
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tok_len = strlen(token_caller) + 1;
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body_len = path_len + tok_len;
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hdr.type = XS_WATCH_EVENT;
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hdr.len = body_len;
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mutex_lock(&adap->dev_data->reply_mutex);
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ret = queue_reply(&staging_q, &hdr, sizeof(hdr));
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if (!ret)
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ret = queue_reply(&staging_q, path, path_len);
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if (!ret)
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ret = queue_reply(&staging_q, token_caller, tok_len);
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if (!ret) {
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/* success: pass reply list onto watcher */
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list_splice_tail(&staging_q, &adap->dev_data->read_buffers);
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wake_up(&adap->dev_data->read_waitq);
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} else
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queue_cleanup(&staging_q);
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mutex_unlock(&adap->dev_data->reply_mutex);
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}
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static void xenbus_worker(struct work_struct *wq)
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{
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struct xenbus_file_priv *u;
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struct xenbus_transaction_holder *trans, *tmp;
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struct watch_adapter *watch, *tmp_watch;
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struct read_buffer *rb, *tmp_rb;
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u = container_of(wq, struct xenbus_file_priv, wq);
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/*
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* No need for locking here because there are no other users,
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* by definition.
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*/
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list_for_each_entry_safe(trans, tmp, &u->transactions, list) {
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xenbus_transaction_end(trans->handle, 1);
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list_del(&trans->list);
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kfree(trans);
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}
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list_for_each_entry_safe(watch, tmp_watch, &u->watches, list) {
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unregister_xenbus_watch(&watch->watch);
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list_del(&watch->list);
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free_watch_adapter(watch);
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}
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list_for_each_entry_safe(rb, tmp_rb, &u->read_buffers, list) {
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list_del(&rb->list);
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kfree(rb);
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}
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kfree(u);
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}
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static void xenbus_file_free(struct kref *kref)
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{
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struct xenbus_file_priv *u;
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/*
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* We might be called in xenbus_thread().
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* Use workqueue to avoid deadlock.
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*/
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u = container_of(kref, struct xenbus_file_priv, kref);
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schedule_work(&u->wq);
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}
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static struct xenbus_transaction_holder *xenbus_get_transaction(
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struct xenbus_file_priv *u, uint32_t tx_id)
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{
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struct xenbus_transaction_holder *trans;
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list_for_each_entry(trans, &u->transactions, list)
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if (trans->handle.id == tx_id)
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return trans;
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return NULL;
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}
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void xenbus_dev_queue_reply(struct xb_req_data *req)
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{
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struct xenbus_file_priv *u = req->par;
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struct xenbus_transaction_holder *trans = NULL;
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int rc;
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LIST_HEAD(staging_q);
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xs_request_exit(req);
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mutex_lock(&u->msgbuffer_mutex);
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if (req->type == XS_TRANSACTION_START) {
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trans = xenbus_get_transaction(u, 0);
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if (WARN_ON(!trans))
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goto out;
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if (req->msg.type == XS_ERROR) {
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list_del(&trans->list);
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kfree(trans);
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} else {
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rc = kstrtou32(req->body, 10, &trans->handle.id);
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if (WARN_ON(rc))
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goto out;
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}
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} else if (req->type == XS_TRANSACTION_END) {
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trans = xenbus_get_transaction(u, req->msg.tx_id);
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if (WARN_ON(!trans))
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goto out;
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list_del(&trans->list);
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kfree(trans);
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}
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mutex_unlock(&u->msgbuffer_mutex);
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mutex_lock(&u->reply_mutex);
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rc = queue_reply(&staging_q, &req->msg, sizeof(req->msg));
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if (!rc)
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rc = queue_reply(&staging_q, req->body, req->msg.len);
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if (!rc) {
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list_splice_tail(&staging_q, &u->read_buffers);
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wake_up(&u->read_waitq);
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} else {
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queue_cleanup(&staging_q);
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}
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mutex_unlock(&u->reply_mutex);
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kfree(req->body);
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kfree(req);
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kref_put(&u->kref, xenbus_file_free);
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return;
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out:
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mutex_unlock(&u->msgbuffer_mutex);
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}
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static int xenbus_command_reply(struct xenbus_file_priv *u,
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unsigned int msg_type, const char *reply)
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{
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struct {
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struct xsd_sockmsg hdr;
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char body[16];
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} msg;
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int rc;
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msg.hdr = u->u.msg;
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msg.hdr.type = msg_type;
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msg.hdr.len = strlen(reply) + 1;
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if (msg.hdr.len > sizeof(msg.body))
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return -E2BIG;
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memcpy(&msg.body, reply, msg.hdr.len);
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mutex_lock(&u->reply_mutex);
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rc = queue_reply(&u->read_buffers, &msg, sizeof(msg.hdr) + msg.hdr.len);
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wake_up(&u->read_waitq);
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mutex_unlock(&u->reply_mutex);
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if (!rc)
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kref_put(&u->kref, xenbus_file_free);
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return rc;
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}
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static int xenbus_write_transaction(unsigned msg_type,
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struct xenbus_file_priv *u)
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{
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int rc;
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struct xenbus_transaction_holder *trans = NULL;
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struct {
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struct xsd_sockmsg hdr;
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char body[];
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} *msg = (void *)u->u.buffer;
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if (msg_type == XS_TRANSACTION_START) {
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trans = kzalloc(sizeof(*trans), GFP_KERNEL);
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if (!trans) {
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rc = -ENOMEM;
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goto out;
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}
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trans->generation_id = xb_dev_generation_id;
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list_add(&trans->list, &u->transactions);
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} else if (msg->hdr.tx_id != 0 &&
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!xenbus_get_transaction(u, msg->hdr.tx_id))
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return xenbus_command_reply(u, XS_ERROR, "ENOENT");
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else if (msg_type == XS_TRANSACTION_END &&
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!(msg->hdr.len == 2 &&
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(!strcmp(msg->body, "T") || !strcmp(msg->body, "F"))))
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return xenbus_command_reply(u, XS_ERROR, "EINVAL");
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else if (msg_type == XS_TRANSACTION_END) {
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trans = xenbus_get_transaction(u, msg->hdr.tx_id);
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if (trans && trans->generation_id != xb_dev_generation_id) {
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list_del(&trans->list);
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kfree(trans);
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if (!strcmp(msg->body, "T"))
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return xenbus_command_reply(u, XS_ERROR,
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"EAGAIN");
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else
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return xenbus_command_reply(u,
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XS_TRANSACTION_END,
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"OK");
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}
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}
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rc = xenbus_dev_request_and_reply(&msg->hdr, u);
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if (rc && trans) {
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list_del(&trans->list);
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kfree(trans);
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}
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out:
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return rc;
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}
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static int xenbus_write_watch(unsigned msg_type, struct xenbus_file_priv *u)
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{
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|
struct watch_adapter *watch;
|
|
char *path, *token;
|
|
int err, rc;
|
|
|
|
path = u->u.buffer + sizeof(u->u.msg);
|
|
token = memchr(path, 0, u->u.msg.len);
|
|
if (token == NULL) {
|
|
rc = xenbus_command_reply(u, XS_ERROR, "EINVAL");
|
|
goto out;
|
|
}
|
|
token++;
|
|
if (memchr(token, 0, u->u.msg.len - (token - path)) == NULL) {
|
|
rc = xenbus_command_reply(u, XS_ERROR, "EINVAL");
|
|
goto out;
|
|
}
|
|
|
|
if (msg_type == XS_WATCH) {
|
|
watch = alloc_watch_adapter(path, token);
|
|
if (watch == NULL) {
|
|
rc = -ENOMEM;
|
|
goto out;
|
|
}
|
|
|
|
watch->watch.callback = watch_fired;
|
|
watch->dev_data = u;
|
|
|
|
err = register_xenbus_watch(&watch->watch);
|
|
if (err) {
|
|
free_watch_adapter(watch);
|
|
rc = err;
|
|
goto out;
|
|
}
|
|
list_add(&watch->list, &u->watches);
|
|
} else {
|
|
list_for_each_entry(watch, &u->watches, list) {
|
|
if (!strcmp(watch->token, token) &&
|
|
!strcmp(watch->watch.node, path)) {
|
|
unregister_xenbus_watch(&watch->watch);
|
|
list_del(&watch->list);
|
|
free_watch_adapter(watch);
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Success. Synthesize a reply to say all is OK. */
|
|
rc = xenbus_command_reply(u, msg_type, "OK");
|
|
|
|
out:
|
|
return rc;
|
|
}
|
|
|
|
static ssize_t xenbus_file_write(struct file *filp,
|
|
const char __user *ubuf,
|
|
size_t len, loff_t *ppos)
|
|
{
|
|
struct xenbus_file_priv *u = filp->private_data;
|
|
uint32_t msg_type;
|
|
int rc = len;
|
|
int ret;
|
|
|
|
/*
|
|
* We're expecting usermode to be writing properly formed
|
|
* xenbus messages. If they write an incomplete message we
|
|
* buffer it up. Once it is complete, we act on it.
|
|
*/
|
|
|
|
/*
|
|
* Make sure concurrent writers can't stomp all over each
|
|
* other's messages and make a mess of our partial message
|
|
* buffer. We don't make any attemppt to stop multiple
|
|
* writers from making a mess of each other's incomplete
|
|
* messages; we're just trying to guarantee our own internal
|
|
* consistency and make sure that single writes are handled
|
|
* atomically.
|
|
*/
|
|
mutex_lock(&u->msgbuffer_mutex);
|
|
|
|
/* Get this out of the way early to avoid confusion */
|
|
if (len == 0)
|
|
goto out;
|
|
|
|
/* Can't write a xenbus message larger we can buffer */
|
|
if (len > sizeof(u->u.buffer) - u->len) {
|
|
/* On error, dump existing buffer */
|
|
u->len = 0;
|
|
rc = -EINVAL;
|
|
goto out;
|
|
}
|
|
|
|
ret = copy_from_user(u->u.buffer + u->len, ubuf, len);
|
|
|
|
if (ret != 0) {
|
|
rc = -EFAULT;
|
|
goto out;
|
|
}
|
|
|
|
/* Deal with a partial copy. */
|
|
len -= ret;
|
|
rc = len;
|
|
|
|
u->len += len;
|
|
|
|
/* Return if we haven't got a full message yet */
|
|
if (u->len < sizeof(u->u.msg))
|
|
goto out; /* not even the header yet */
|
|
|
|
/* If we're expecting a message that's larger than we can
|
|
possibly send, dump what we have and return an error. */
|
|
if ((sizeof(u->u.msg) + u->u.msg.len) > sizeof(u->u.buffer)) {
|
|
rc = -E2BIG;
|
|
u->len = 0;
|
|
goto out;
|
|
}
|
|
|
|
if (u->len < (sizeof(u->u.msg) + u->u.msg.len))
|
|
goto out; /* incomplete data portion */
|
|
|
|
/*
|
|
* OK, now we have a complete message. Do something with it.
|
|
*/
|
|
|
|
kref_get(&u->kref);
|
|
|
|
msg_type = u->u.msg.type;
|
|
|
|
switch (msg_type) {
|
|
case XS_WATCH:
|
|
case XS_UNWATCH:
|
|
/* (Un)Ask for some path to be watched for changes */
|
|
ret = xenbus_write_watch(msg_type, u);
|
|
break;
|
|
|
|
default:
|
|
/* Send out a transaction */
|
|
ret = xenbus_write_transaction(msg_type, u);
|
|
break;
|
|
}
|
|
if (ret != 0) {
|
|
rc = ret;
|
|
kref_put(&u->kref, xenbus_file_free);
|
|
}
|
|
|
|
/* Buffered message consumed */
|
|
u->len = 0;
|
|
|
|
out:
|
|
mutex_unlock(&u->msgbuffer_mutex);
|
|
return rc;
|
|
}
|
|
|
|
static int xenbus_file_open(struct inode *inode, struct file *filp)
|
|
{
|
|
struct xenbus_file_priv *u;
|
|
|
|
if (xen_store_evtchn == 0)
|
|
return -ENOENT;
|
|
|
|
stream_open(inode, filp);
|
|
|
|
u = kzalloc(sizeof(*u), GFP_KERNEL);
|
|
if (u == NULL)
|
|
return -ENOMEM;
|
|
|
|
kref_init(&u->kref);
|
|
|
|
INIT_LIST_HEAD(&u->transactions);
|
|
INIT_LIST_HEAD(&u->watches);
|
|
INIT_LIST_HEAD(&u->read_buffers);
|
|
init_waitqueue_head(&u->read_waitq);
|
|
INIT_WORK(&u->wq, xenbus_worker);
|
|
|
|
mutex_init(&u->reply_mutex);
|
|
mutex_init(&u->msgbuffer_mutex);
|
|
|
|
filp->private_data = u;
|
|
|
|
return 0;
|
|
}
|
|
|
|
static int xenbus_file_release(struct inode *inode, struct file *filp)
|
|
{
|
|
struct xenbus_file_priv *u = filp->private_data;
|
|
|
|
kref_put(&u->kref, xenbus_file_free);
|
|
|
|
return 0;
|
|
}
|
|
|
|
static __poll_t xenbus_file_poll(struct file *file, poll_table *wait)
|
|
{
|
|
struct xenbus_file_priv *u = file->private_data;
|
|
|
|
poll_wait(file, &u->read_waitq, wait);
|
|
if (!list_empty(&u->read_buffers))
|
|
return EPOLLIN | EPOLLRDNORM;
|
|
return 0;
|
|
}
|
|
|
|
const struct file_operations xen_xenbus_fops = {
|
|
.read = xenbus_file_read,
|
|
.write = xenbus_file_write,
|
|
.open = xenbus_file_open,
|
|
.release = xenbus_file_release,
|
|
.poll = xenbus_file_poll,
|
|
.llseek = no_llseek,
|
|
};
|
|
EXPORT_SYMBOL_GPL(xen_xenbus_fops);
|
|
|
|
static struct miscdevice xenbus_dev = {
|
|
.minor = MISC_DYNAMIC_MINOR,
|
|
.name = "xen/xenbus",
|
|
.fops = &xen_xenbus_fops,
|
|
};
|
|
|
|
static int __init xenbus_init(void)
|
|
{
|
|
int err;
|
|
|
|
if (!xen_domain())
|
|
return -ENODEV;
|
|
|
|
err = misc_register(&xenbus_dev);
|
|
if (err)
|
|
pr_err("Could not register xenbus frontend device\n");
|
|
return err;
|
|
}
|
|
device_initcall(xenbus_init);
|